1. Field of the Invention
The present invention relates to a dry vacuum pump, and more particularly to a complex dry vacuum pump having a root rotor and a screw rotor.
2. Description of the Prior Art
A dry vacuum pump have according to the state of the art includes at least one root rotor having a lobe and at least one screw rotor so as to keep a complete vacuum state in a process chamber and reduce costs of required power. The root rotor is connected with the process chamber so as to be used for sucking and compressing process by-products, including gaseous material generated in the process chamber. The screw rotor is used for discharging gas and process by-products, which are sucked by the root rotor, to an exterior of the process chamber. Under any circumstance, these rotors are operated in an airtight state so as to keep a vacuum state in the process chamber.
In general, a septal wall is provided between the side of such root rotors and the side of such screw rotors so as to cause process by-products not to interrupt rotation of the rotors and to smoothly move from the group of the root rotors to the group of the screw rotors. A representative embodiment of such a structure is disclosed in U.S. Pat. No. 5,549,463 filed in the name of Kashiyama Industry Co., Ltd (hereinafter, referring to FIG. 9).
According to this patent document, a dry vacuum pump 100 includes a pair of root rotors 102 and 103 and a pair of screw rotors 105 and 106. The pair of root rotors 102 and 103 and the pair of screw rotors 105 and 106 are driven by a single driving motor 200. A septal wall 108 is provided between the root rotors 102 and 103 and the screw rotors 105 and 106 so as to cause the above-mentioned process by-products from a process chamber (not shown) not to be directly transferred to the screw rotors 105 and 106. This patent document is included in the present document as a reference of the present invention.
However, a septal wall 108 required for a dry vacuum pump 100 disclosed in U.S. Pat. No. 5,549,463 is disposed between root rotors 102 and 103 and screw rotors 105 and 106. Particularly, a housing 107 including these rotors has to be divided into several parts. This increases the effort to manufacture such a dry vacuum pump and a number of components thereof.
Furthermore, additionally to a scheme using a septal wall, a scheme using a screw of a variable pitch has been attempted in a dry vacuum pump using screw rotors, so as to reduce amount of power consumption and increase the amount of a by-product which is pressed and discharged. However, this scheme needs a larger rotor and pump housing in comparison with a conventional scheme, thereby decreasing effectiveness.
Furthermore, a scheme allowing a root rotor and a screw rotor to be directly connected with each other without a septal wall disposed between them has been attempted. However, in this case, the root rotor and the screw rotor had to be designed in such a manner as to have sections similar to each other so as to increase gas compression transfer efficiency.
However, in a case of a root rotor and a screw rotor being designed in a similar shape, a negative effect is exerted on balance between the root rotor and the screw rotor, thereby causing serious vibration and noise in a vacuum pump.
Also, as shown in FIG. 9, a driving motor 200 used in a vacuum pump includes a stator 220, a rotator 230, a shaft 240, and a motor case 210.
When a conventional vacuum pump having such a structure is operated, a pair of root rotors 102 and 103 and a pair of screw rotors 105 and 106, which are in the interior of the vacuum pump, are rotated by driving of the driving motor 200, so that process by-products are sucked through a suction opening (not shown) of the vacuum pump, pass through the interior of the vacuum pump, and are discharged via a discharge opening (not shown). Therefore, a process chamber of an apparatus for manufacturing a semiconductor and a display is put in a vacuum state. In this time, when process by-products sucked by rotation of the pair of root rotors 102 and 103 and the pair of screw rotors 105 and 106 pass through the interior of the vacuum pump and are discharged via a discharge opening, a part of the process by-products flow in the interior of the driving motor 200. The process by-products flowing in the interior in such a manner cause damage of a stator coil 220a so that the lifecycle of the driving motor 200 is reduced.
Therefore, a can 400 is installed between a stator 220 and a rotator 230 so as to prevent damage of a stator coil 220a caused by process by-products flowing from a conventional vacuum pump. Such a can 400 is a sheet made of material such as stainless steel, etc., and is welded in a circular shape. The can 400 is installed between the stator 220 and the rotator 230, thereby preventing damage to the stator coil 220a due to process by-products or lubricating oil flowing from the vacuum pump.
However, the can 400 installed between the stator 220 and the rotator 230 has to be disposed in a minute gap between the stator 220 and the rotator 230, so it is difficult to manufacture and assemble the can 400.
Also, the can installed between the stator 220 and the rotator 230 causes loss of own power of a motor, so that a large amount of power consumption of the motor is caused, thereby increasing operation costs.